The present invention relates to a turbine expansion machine equipped with a variable nozzle mechanism.
A turbine expansion machine is used to increase the thermal efficiency of a helium refrigerator, and a variable nozzle drive mechanism is proposed to vary the capacity of the turbine expansion machine (see, for example, Japanese Patent No. 72805/1991 and unexamined Japanese Patent Publication No. 137101/1994).
The expansion turbine variable-nozzle drive apparatus of Japanese Patent No. 72805/1991 is, as shown in FIG. 1, provided with a rod 9 that can move linearly and is equipped with a junction portion 9a configured with a knob 8a disposed on the outer periphery of a movable ring 8. The knob 8a has an arched, elevated surface in both directions of the rod""s movement, and a grooved surface is provided on junction portion 9a that can engage with the arched surfaces of the knob. In FIG. 1, part numbers show a main unit of an expansion turbine as 1, an air cylinder as 2, a nozzle drive apparatus as 3, a nozzle fixing ring as 4, a variable nozzle as 5, a fixing pin as 6, and a movable pin as 7. By rotating variable ring 8, movable pin 7 is driven circumferentially, whereby the angle of variable nozzle 5 is varied.
The variable nozzle-type expansion turbine according to the unexamined Japanese patent publication No. 137101/1994 is comprised of, as shown in FIG. 2, a main shaft 11 at one end of which a turbine impeller 12 is disposed and at the other end of which a brake fan 13 is mounted. Main shaft 11 is supported by a journal bearing and a thrust bearing. The turbine impeller 12 is installed outside a vacuum refrigerating tank 14 (vacuum vessel) to which the casing 15 of the expansion turbine is fixed.
In the above-mentioned conventional turbine expansion machine and its variable nozzle drive mechanism, nozzle drive apparatus 3 for driving variable nozzle 5 is arranged at a normal-temperature portion outside vacuum vessel 14, a low-temperature portion is enclosed with a heat insulation material, and a nozzle drive plate (movable ring 8 ) is driven. However, one problem affecting the machine and the mechanism disclosed is the ingress of excessive heat into the low-temperature portion.
More explicitly, in the above-mentioned examples, the main unit 1 of the expansion turbine (or a casing 15 of the expansion turbine) is installed in the normal-temperature portion, inside of which the turbine impeller 12 is assembled to adiabatically expand helium. Therefore, when the helium gas at a cryogenic temperature (for instance, 7xcx9c9K) is expanded adiabatically at the turbine impeller 12, the gas is heated by heat entering from the main unit of the expansion turbine 1, so the adiabatic efficiency of the turbine expansion machine deteriorates, which is a practical problem.
To solve these problems, it is also possible to install in the cryogenic temperature portion in the vacuum vessel all of main unit 1 of the expansion turbine, nozzle drive apparatus 3, variable nozzle 5, movable ring 8, turbine impeller 12, etc., thereby heat-insulating them from the outside, normal-temperature region. However, the mechanical portion of nozzle drive apparatus 3 becomes difficult to maintain and an actuator (motor or pneumatic cylinder) of nozzle drive apparatus 3 must be specially structured to withstand operations at a cryogenic temperature and in a vacuum environment. Therefore, maintenance becomes very difficult and the cost of the system is extremely high.
The present invention aims to solve these problems. That is, an object of the present invention is to provide a turbine expansion machine with a variable nozzle mechanism wherein most of the actuator and the nozzle drive mechanism can be installed in the normal-temperature range at atmospheric pressure, heat input can be suppressed to the extremely minimal level while driving the variable nozzle of the expansion turbine, whereby helium gas at a cryogenic temperature can be expanded adiabatically at a high adiabatic efficiency.
In accordance with a preferred embodiment of the present invention, there is provided a turbine expansion machine with variable nozzle mechanism. The machine comprises a vacuum vessel, an adiabatic expansion apparatus, a control device and a variable nozzle mechanism. The adiabatic expansion apparatus is disposed in the vacuum vessel, and includes a turbine impeller having an axis wherein the impeller is arranged to adiabatically expand gas when rotated. The control device is disposed outside the vacuum vessel, and operably connected coaxially with the turbine impeller to control the impeller. The variable nozzle mechanism defines a variable throat area for gas introduced into the turbine impeller. The variable nozzle mechanism further comprises a nozzle component disposed in the adiabatic expansion apparatus, a driving component installed outside the vacuum vessel, and a coaxial, thin cylindrical component, operably connecting the nozzle component and the driving component to the turbine impeller, wherein the nozzle component is driven by rotating the cylindrical component about the axis of the turbine impeller.
According to another embodiment of the present invention, a turbine expansion machine is provided with a variable nozzle mechanism comprising a built-in turbine impeller (12), an adiabatic expansion apparatus (22) that adiabatically expands gas at a cryogenic temperature when the impeller rotates, a control device (24) that is connected coaxially with the turbine impeller and controls the impeller, and a variable nozzle mechanism (30) that changes the throat area of the gas at cryogenic temperature to be introduced into the turbine impeller. The adiabatic expansion apparatus is installed in vacuum vessel (14), the control device is equipped outside the vacuum vessel, the variable nozzle mechanism is composed of nozzle component (32) built into the adiabatic expansion apparatus and drive component (34) disposed outside the vacuum vessel. The nozzle component and the drive component are connected to the turbine impeller with a coaxial thin cylindrical component (36), and the nozzle component is driven by the cylindrical component when it swings around the axis of the turbine impeller.
According to the configuration of the present invention, because the adiabatic expansion apparatus (22) with turbine impeller (12) is installed in vacuum vessel (14), heat input can be suppressed to a minimum due to vacuum heat insulation. Since control device (24), which controls the turbine impeller, is arranged outside the vacuum vessel, the control device can be easily maintained. Furthermore, the variable nozzle mechanism (30), which varies the throat area of the turbine impeller, is composed of nozzle component (32) incorporated inside the adiabatic expansion apparatus and drive component (34) installed outside the vacuum vessel. Because the nozzle component (32) and the drive component (34) are connected with thin cylindrical component (36) which drives the nozzle component, the cylindrical component can be made thin enough to drive the nozzle component (for example, about 0.5 mm thick), so that the amount of heat transmitted from the cylindrical component can be reduced to the extremely minimal level. Consequently, most of the actuator and the nozzle drive mechanism can be installed in a normal-temperature environment at atmospheric pressure and heat input can be kept extremely low, and the variable nozzle of the expansion turbine can be driven. Thereby helium gas at a cryogenic temperature can be expanded adiabatically at a high adiabatic efficiency.
According to a further preferred embodiment of the present invention, the aforementioned nozzle component (32) comprises a plurality of movable nozzle plates (38) disposed around the turbine impeller (12) and supported by supporting pins (37) in a movable manner, and a driving circular disk (39), which is connected to the above-mentioned cylindrical component (36), and also to each movable nozzle plate by means of a drive pin (39a), wherein the aforementioned driving component (34) is configured with a large gear (40) that is connected to the outer periphery of the above-mentioned cylindrical component (36) and can turn around the axis of the turbine impeller, and a rotary drive device (42) that rotates and drives a small gear (41) engaged with the large gear.
Using this configuration, cylindrical component (36) can be adjusted about the axis of the turbine impeller by rotary driving device (42) via small gear (41) and large gear (40), thus driving circular disk (39) is also controlled, movable nozzle plate (38) is driven to turn, and the throat area of the variable nozzle can be varied continuously.
The aforementioned rotary driving device (42) is a pulse motor, and preferably should be provided with a position detection sensor (43) for detecting the rotary limit of large gear (40). In this configuration, the reference position of variable nozzle (38) is detected by position detection sensor (43), and the swing angle of driving circular disk (38) from the reference position is precisely determined by the pulse motor, so that the variable nozzle can be accurately positioned.
The above-mentioned adiabatic expansion apparatus (22) is connected to control device (24) by means of inner cylindrical component (25a), outer cylindrical component (25b) and cylindrical component (36). The inner and outer surfaces of cylindrical component (36) are sealed by sealing components (44a, 44b), respectively, in a slidable manner. In this configuration, heat input from a portion maintained at a normal temperature into adiabatic expansion apparatus (22) can be suppressed to a minimal level by outer cylindrical component (25b), inner cylindrical component (25a), and inner heat insulation component (23). The sealing components (44a, 44b) can prevent the flow of heat from low-temperature impeller (12) to the normal-temperature side through gaps between inner cylindrical component (25a) and cylindrical component (36) and between inner heat insulation component (23) and cylindrical component (36). Therefore, ingress of heat can be prevented.
The above-mentioned control device (24) should preferably be a generator or a compressor impeller. When a generator is used for control purposes, the energy loss produced during adiabatic expansion can be collected as electric power. When a compressor impeller is used for control purposes, energy loss at this time can be recovered as a pressurized gas.
These and other objects and advantages of the present invention will become more readily appreciated and understood from a consideration of the following detailed description of the preferred embodiments when taken together with the accompanying drawings.